ISO 228-155° flankpipe thread
British Standard Pipe (parallel) Threads
The parallel pipe thread marked G. Threads are Whitworth form at 55 degrees, so a G thread does not interchange with NPT even at the same nominal size — 1/2 in the two systems is a different diameter and a different pitch. 11 designations are listed here, all quoted in inches.
Dimensions11 sizes
| Designation | TPI | Major (in) | Pitch Ø (in) | Minor ext (in) | Tap drill (in) |
|---|---|---|---|---|---|
| 1/8-28 BSP | 28 | 0.383 | 0.3602 | 0.3374 | 0.3473 |
| 1/4-19 BSP | 19 | 0.518 | 0.4843 | 0.4508 | 0.4654 |
| 3/8-19 BSP | 19 | 0.656 | 0.6224 | 0.5886 | 0.6034 |
| 1/2-14 BSP | 14 | 0.825 | 0.7791 | 0.7335 | 0.7536 |
| 5/8-14 BSP | 14 | 0.902 | 0.8563 | 0.8106 | 0.8306 |
| 3/4-14 BSP | 14 | 1.041 | 0.9953 | 0.9496 | 0.9696 |
| 7/8-14 BSP | 14 | 1.189 | 1.1433 | 1.0976 | 1.1176 |
| 1-11 BSP | 11 | 1.309 | 1.2508 | 1.1925 | 1.2181 |
| 1-1/4-11 BSP | 11 | 1.65 | 1.5917 | 1.5335 | 1.5591 |
| 1-1/2-11 BSP | 11 | 1.882 | 1.8236 | 1.7657 | 1.7911 |
| 2-11 BSP | 11 | 2.347 | 2.289 | 2.2307 | 2.2561 |
Sizes are nominal bores, not diameters — 1/8 measures 0.383 in across the thread.